Method of making metallic magnesium



Dec. 29 1925. 1,567,318

P. COTTRINGER ET AL METHOD OF MAKING METALLIC MAGNESIUM Filed May 21. 1923 INVENTORJ' ATTZRA/Ei Patented Dec. 29, 1925.

: -..um1-1-:o s'rA'i asj PATENT OFFICE.

' rain: corrnmenn AND snnnnon B. HEATH, or mn'iiiann,

'HICHIGAN, ASSIGNORS 130 THE DOW CHEMICAL COMPANY, OI MIDLAND. MICHIGAN, A CORPORATION 01 mcarem. g

HETHOD OF MAKING METALLIC MAGNESIUM.

" Application and m 21, ms. Serial No. 640,344,;

To all whom; it may concern:

Be it known that we, PAUL Corrnmonn and SHELDON B. HEATH, citizens of the recognized as essential all universally accepted ple change in manipulation or procedure without reconstruction of existing types of' United States, and residents of Midland,

county of Midland, and State of Michigan, have jointly invented a new and useful Improvement in Methods of Making Metallic Magnesium, of which the following is a specification, the principle of the invention being herein explained and the best mode in which we have contemplated applfying that principle so as to distinguish it rom other inventions.

In the electrolytic production of metallic magnesium the chloride of the metal was first used and is presumably still most extensively employed, although the electrolysis of the fluoride in connection with which it is possible to utilize magnesium oxide or -magnesium sulphide as the raw material source has been developed as a collateral method (see J. Billiter, Die elecktro-chem ischem Verfahren der chemischem Gross-Industrie, Halle 1918, Bd. III, pp. 95, 104). In the utilization of magnesium chloride for the electrolyte it has from the first been that only the anhydrous form would serve and that any traces of moisture were highly detrimental. Detrimental reactions are produced whereeither water ormagnesium sulphate is included in such. electrolyte and have been fully investigated by F. Oettel among others, as will be found fully recorded in Billiters work above cited, .and so a discussion of such actions need not be entered upon here. It will sufiice, in other words, to note that the view and practice has required the use of anhydrous magnesium chloride for the electrolytic bath in the.

process under consideration, this despite the well recognized dilficulty and expense in volved in the preparation of such anhydrous chloride. j

In the light of the foregoing we have made the surprising discovery and invention that magnesium chloride in its various hydrated forms maybe successfully introduced directly into an electrolytic cell to produce metallic magnesium and that this esult may be achieved by a relatively simcell or pp ratu cilitate it p pal e ement a cast To the accomplishment of the foregoing and related ends our invention then consists of the steps hereinafter fully described and partlcularly pointed out in the claims, the annexed drawing and following description llustrating but several of the various wavs 1n WhlCll the principle of the invention may be carried out.

In said annexed drawing Fig. 1 is a more or less diagrammatic representation of one familiar type of electrolytic cell as heretofore used in the production of metallic magnesium and adapted for such use 1110111 lmproved method or process; and Figs. 2 and 3 are similar representations of other forms of cell or apparatus similarly adapted for use in our method or process.

As is well known, magnesium chloride normally crystallizes out with six molecules of water according to the formula MgCl fi- H O. While some trouble is encountered in the preliminary or partial dehydration of the salt, it is relatively simple and inexpensive to reduce the water of crystallization to two molecules since this can be acoomphshed by various methods of heating the salt. However, in order to eliminate the final two molecules of water, or in other words, produce the anhydrous salt heretofore required for use in the connection in hand, it has been necessary to conduct the heating or drying operation in an atmosphere of hydrochloric acid gas, which is obviously expensive and tedious. As already indicated, in our present improved method the fully hydrated form having six mole-' cules of water.

Where the latter is utilized i't Wlll preferably, although not necessarily,

beadded to the cell as hereinafter described in fused or molten condition, while the intermediate hydrates will be conveniently utilized in granulated form as this will fathe addition of the material to the cell or electrolytic apparatus in properly regulated amount.

The form of apparatus illustrated in Fig. 1 is substantially that shown .and described originally by A. Graetzel (see German Patent No. 27,962 of 1883) and comprises as ir o teel i.=:-vessel 1 that constitutes the cell proper and in which theclectrolyte is'placed and maintainedinmolten condition. Vessel 1 at the same time constitutes the cathode, and for.

the purpose of initially melting the electrolyt the vessel may be su ported in a suitable furnace chamber iiot shown). From a suitable cover or rather bridge 2 that spans the upper end of vessel 1 is supported an annular diaphragm or partition 3 of orcelain, fireclay or equivalent material wh1ch serves to laterally surround the carbon or graphite anode 4. It will be noted that such diaphragm or partition does not extend entirely down to the bottom of the vessel and that while the upper end of the space between such partition and the anode is normally covered over by segmental plates 5 the latter are removable in order to afford access to such space when desired. A suitable duct is also connected with such upper end of this space in order to conduct away any gases arisingl from the anode compartment defined by t e aforesaid annular diaphragm or curtain.

When starting operation of the foregoing type of cell in accordance with our present process we place in the vessel 1, constituting the cell proper, a suitable quantity of anhydrous magnesium chloride. which has mixed therewith the usual and well-known proportions of other chlorides required to give the bath when melted down the necessary density to cause the magnesium metal to float instead of sink in such bath. Thus, one formula for such a mixture as prescribed in German Patent No. 115,015, such formula being designed to utilize naturally occurring carnallite, will be MgCl .KCl.NaCl having av content of approximately 41.66 per cent of magnesiumchloride, 32.66 per cent of potassium chloride and 25.66 per cent of sodium chloride or common salt, and a density of approximately degrees B. (s gr. 1. 1154); It is also possible to use a ormula in which potassium chloride is entirely omitted, the amounts of the two other chlorides being in the aggregate that much'larger e. g. from 60 to per cent of magnesium chloride and from 40 to 80 per cent of sodium chloride, with a small percentage of calcium fluoride to cause the magnesium metal as it is freed from the electrolyte to coalesce.

Upon passing a suitable electric current through the foregoing apparatus with the cell charged with such mixture of chlorides, including anhydrous magnesium chloride,

chlorine is generated at the anode and rising inside of the annular partition surrounding. same, escapes through the duct that leads from the space included within such partition, while metallic magnesium is generated fidJfiCGIlt to the inner wall of the vessel that constitutes the cathode and rises ation.

to the surface of the electrolytic bath where it agglomerates into a mass or masses and may be removed as by means of a ladle from time to time; the chlorides that con stitute the bath forming a protective film to revent oxidation thereof.

ccording to the present practice, as the electrolysis gfoceeds the stock of anhydrous magnesium c loride in the bath is replenished by adding more of the same to the oathover the metal as it thus floats in the bath,

ode compartment of the cell i. e. that portion lying between the walls of the vessel within the anode compartment defined by,

the annular diaphragmor partition 3 in the case of the particular cell under consider- If the normal hexahydrate salt is thus introduced a certain explosive effect will be noted although not sufliciently severe to disarrange the apparatus, while in the case of the lower hydrate the introduction thereof occasions no disturbance whatever. What is more important, any of the hydrated forms may be introduced Without any of the untoward results following which have heretofore al- .ways invariably been noted where it was attempted to electrolyze a hydrated form of magnesium chloride. We find it desirable to intermix with such hydrated chloride a small percentage of finely divided carbon, such as powdered coke, e. g. with the hexahydrate three per cent of carbon will be included, while in the case of the di-hydrate but little more than a trace has been. used.

We are not prepared to give the theoretical reasons for the smooth and satisfactory dissociation that we-obtain but it is probable that the nascent chloride as generated at the anode coming into contact with the hydrated magnesium chloride immediately upon its introduction into the bath suppresses any tendency on the part of the latter to re-act with production of magnesium oxide, magnesium oxychloride, or other deleterious compounds. The water of crystallization from the added salt driven off, or forms hydrochloric acid, and rises as a vapor along with any excess chlorine gas thus generated at the anode, while the chloride thus dehydrated passes down and.

into the cathode compartment where it is .dissociated as before.

Themodified form'of cell shown in Fig. 2, differs from the one just described in that the vessel 6 constituting the body of I 1s supported I'adjacent one end wall of the cell. e an-- 4 and the cathode. H Y this form of cell is substantially identical is; here not employed .as the cathode, separate" iron cathode,"- 7

ode 8 as before consists of a carbon or graphite rod 8'that depends into the electrolyte in the cell and a:- transverse septum or partition 9 is interposedbetweenj-such anode I he {mode of operation of with that of Fig. 1, the deviation from the current practice consisting inthe utilization hydrated instead of the anhydrous chloride, such'hydrated material being in troduced in the compartment wherein the anode is located.

It is also possible to utilize the hydrated forms of magnesium chloi'ide in that type of electrolytic apparatus wherein the magfrom the latter by occurs at-. a ly adjacent electroafterwards recovered secondary electrolysis. (See Fig. 3). The electro-positive metals proposed .for this purpose include copper, aluminum, tin, lead and ordinarily an electrolytic apparatus'comprising twin cells 10 and 11 is utilized, each having as bottom a body 12 of such electro-positive metal in molten condition and a bath 13 of the electrolyte resting upon such molten metal. The bodies of the two cells are electrically interconnected and the primary cell is o erated with one or more carbon electrodbs 14 constituting the anode and the secondary nesium is received into some more positive metal and cell with one or more iron electrodes 15 constituting the cathode. During the assage of the current, at suitable intervals t e alloy is interchanged between the secondary cell and th added to the primary cell as required and the magnesium metal being withdrawn from the secondary cell. Y

Heretoforein the operation of this type of apparatus, just as in the case of the previously described and similar forms of cell, it has been considered strictly essential that the magnesium chloride introduced into the primary cell be in the anhydrous form. It is nevertheless quite permissible in accord ance with our discovery in an apparatus of this type to introduce the hydrated-form of the chloride, providing such introduction point or points sufliciently closeto the anode or anodes to permit the chlorine there generated to inhibit the decomposition of the freshly infi'oduced electrolyte. \Vhile our improved process has been described with particular reference to the elec-v trolytic production of metallic magnesium from the chloride ot themtal, it'will be understood that thesame principle applies to the similar production of other metals whose chlorides form hydrates so that dehydration has heretofore been found necessary prior to introduction of such chlorides into the ing that the e primary cell, the electrolyte being as previously indicated, the material will be prepared in comminuted form either by flaking, grinding or otherwise; or, in the case of the hexahydrate,'which is readily fusible, it may be introduced in molten condition, which permits equally ready and convenient control of the rate of feed. Such rate, without becoming excessive, will suffice to replace the chloride dissociated by the electrolysis,

material should not be supplied so fast as to collect on or cake over the body of electrolyte exposed in the anode compartment. The ebullition of gas in such compartment we have found serves to intermix the material, if supplied at the proper rate, with such electrolyte.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the method herein disclosed. provided the step or steps stated by any of the following claims or the equivalent of such stated step, or steps be employed.

We therefore particularly point out and distinctly claim as our invent1on:

1. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and introducing more magnesium chloride into such bath adjacent the anode.

2. In the production of metallic magnosium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and introducing more magnesium chloride containing water of crystallization into such bath adjacent the anode.

3. In the production of metallic magnesium, the steps which consist in elcctrolyzing a molten bath including magnesium chloride,

magnesium, the steps which consist in electrothe important consideration belyzing a molten bath including magnesium chloride, and gradually introducing more magnesium chloride containing water of crystallization into such bath adjacent the anode.

6. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride and introducing more magnesium chloride containing water of crystallization into such bath adjacent the. anode, the rate of such introduction being graduated to prevent such material from collecting on or caking over the bath. I I

7. In the productionof metallic magnesium, the -stepswhich consist in electrolyzing a molten bath including magnesium chloride, and introducing more magnesium chloride into such bath adjacent the anode, a small percentage of carbon being intermixed with such chloride.

8. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and gradually introducing more magnesium chloride into such bath adjacent the anode, a small percentage of carbon being intermixed with such chloride.

9. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and introducing more magnesium chloride containing water of crystallization into such bath adjacent the anode, a small percentage of carbon being intermixed with such chloride.

10. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and gradually introducing more magnesium chloride containing water of crystallization and a small percentage of carbon into such bath adjacent the anode.

11. In the production of metallic magnesium, the steps which consist in electrolyzing a molten bath including magnesium chloride, and introducing more magnesium chloride containing water of crystallization and a small percentage of carbon into such bath adjacent the anode, the rate of such introduction being graduated to prevent such material from collectingon or caking over the bath.

12. In the production of metallic magnesium, the steps which consist in electrolyz" ing a molten bath including magnesium chloride, and; introducing more magnesium chloride containing water of crystallization into such bath adjacent the anode, such added chloride being in molten condition.

13. In the production of metallic magelectric current through a molten bath ineluding magnesium chloride, such current passing from a carbon anode to a metal,

cathode and such anode being laterally surrounded by a wall forming a compartment therefor," and adding magnesium chloride containing waterof crystallization to such bath by introducing same into such'anode compartment.

15. In the production of metallic mag-- nesium, the steps which consist in passing an electric current through a molten bath including magnesium chloride, such current passing from a carbon anode to a metal cathode and such anode being laterally surrounded by a wall forming a compartment therefor, and gradually adding magnesium chloride containing water of crystallization to such bath by introducing same into such anode compartment.

16. The method of utilizing the hydrated forms of metallic chloride in the electro-' lytic production of the corresponding metal, which consists in subjecting such chloride to the action of the chlorine evolved in the electrolysis.

17. The method of utilizing the hydrated forms of metallic chloride in the electrolytic production of the corresponding metal, which consists in subjecting such chloride intermixed with a small percentage of carbon I to the action of the chlorine evolved in the electrolysis.

18. The method of utilizing the hydrated forms of magnesium chloride in the electrolytic production of metallic magnesium, which consist in subjecting such chloride to the action of the chlorine evolved in theelectrolysis.

19. The method of utilizing the hydrated forms of magnesium chloride in the electrolytic production of metallic magnesium, which consists in subjecting such chloride intermixed with a small percentage of carbon to the actionof the chlorine evolved in the electrolysis.

Signed by us, this 1 8th-day of May, 1923.

PAUL COTTRINGER. SHELDON B. HEATH. 

